Improve semantics of argument terminator ("--") and avoid consuming it unnecessarily

• Poetry version: Poetry (version 1.2.2)
• Python version: Python: 3.10.7
• OS version and name: Debian bookworm
• pyproject.toml:
• e.g.

streamlit = "^1.15.1"

• I am on the latest stable Poetry version, installed using a recommended method.
• I have searched the issues of this repo and believe that this is not a duplicate.
• I have consulted the FAQ and blog for any relevant entries or release notes.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option) and have included the output below.

Issue

Using poetry run it is possible to run commands which themselves might accept a -- e.g.

poetry run '--' streamlit run demo.py '--' --script-args

However, it can be the case that the first -- is omitted. In this case, poetry run is able to infer from the fact that it is not given a flag to start parsing the program and its arguments, however, it will still eat the first -- rather than passing it on. So if we run:

poetry run streamlit run demo.py '--' --script-args

Then --script-args will be passed to streamlit, which is not what we wanted. Poetry should only eat the -- before it has started parsing the program arguments.

Start with the poetry run command entry point and reproduce both examples from the issue, including the quoted -- arguments. Trace when poetry run begins parsing the program arguments; done means a terminator after parsing has started is passed through, while a terminator before parsing is consumed.